In known oxidation furnaces of this type, the deflecting rollers may be arranged either in the interior of the housing or outside the housing. In this case, the air infeed device is configured such that hot air is emitted into a region between the deflecting rollers and the process chamber, in a direction towards the process chamber. This has the effect that the carbon fibres cool somewhat as they pass over a deflecting roller, since they have left the process chamber and moreover are no longer acted upon by hot air emitted by the air infeed device.
This means that, once the fibres have been deflected by a deflecting roller and re-enter the process chamber, some of the energy of the furnace has first to be applied to re-heating the fibres to the temperature required for the oxidation procedure.
In particular, if the deflecting rollers are located outside the furnace housing in the ambient atmosphere of the oxidation furnace, a high percentage—which in extreme cases may be up to 80%—of the energy required for operating the oxidation furnace may be consumed purely in heating the fibres up to the required oxidation temperature again.
It is thus an object of the invention to provide an oxidation furnace of the type mentioned at the outset in which the use of energy is more favourable.